1. Field of the Invention
This invention relates to photographic lens systems, and more particularly, to lens systems adapted for use in three-dimensional cinematography.
2. Description of the Prior Art
Three dimensional motion picture photography is old in the art. Many devices are known for photographing images from two positions separated by an interocular distance to place right- and left-hand adjacent images onto a frame of a film strip, side-by-side or one above the other. Bernier, U.S. Pat. No. 3,531,191, the disclosure of which is incorporated by reference herein, discloses an attachment for a conventional motion picture camera to permit the filming of stereoscopic images on motion picture film. The images are placed one above the other, rather than side-by-side.
The Bernier attachment comprises a pair of wide angled right and left eye displacement prisms which receive right and left eye images side by side and then transpose these images into vertical relationship on the film. The right and left eye images together occupy the same area on the film normally occupied by a single photographic frame. Immediately behind the prisms and part of the same attachment are two lens systems which gather the right and left eye images and focus them on the film plane. The two lens systems should be of the same equivalent focal length and in focus together so that the right and left eye images are on the same scale. The prisms and the lenses must fit tight packaging constraints in order to be mounted on a conventional motion picture camera. The prisms are folded to clear the flange requirements of the particular camera being used and the lens systems are actually located in the interior of the camera body. The prisms and lens systems of the three dimensional photography attachment must fit in the space normally occupied by a single lens system when the camera is not being used for three-dimensional cinematography.
The Bernier invention provided apparatus for attachment to a conventional motion picture camera such as the Mitchell BNC camera. This camera is a viewfinder camera and is being superseded by reflex motion picture cameras such as the Panaflex, Arriflex and Eclair reflex cameras. In reflex motion picture cameras the cameraman views the scene through the same optical system that projects the image onto the motion picture film, rather than through a separate viewfinder incorporating a completely separate lens system. The cameraman may thus see the scene the film sees and adjust focus and convergence as required. Such cameras present tighter and more exacting packaging problems compared to non-reflex motion picture cameras owing to the space occupied by the reflex mirror and often to smaller camera flange diameters. Thus, both the displacement prisms of the Bernier system and the lenses provided therewith must fit into a smaller space than is the case with the viewfinder Mitchell camera and the like. The reflex mirror requires increased back focal lengths for lenses in reflex cameras. Another factor requiring minimization of the size of the prisms and lenses of the Bernier type optical attachment for use with modern reflex cameras is the weight of the overall system, which should be decreased for greater portability and convenience of use.
The lens system used with non-reflex motion cameras such as the Mitchell BNC is typified by the trioptiscope lens system which has four elements in three groups (the rearmost group consists of two elements cemented together). This lens system is incapable of fitting into the three dimensional photography attachment necessary for reflex motion picture cameras due to mechanical interference with the reflex mirror as well as other portions of the camera. In addition, the lenses provided for use with the Bernier attachment for non-reflex motion picture cameras have not been available in a variety of focal lengths. Three dimensional cinematography would be materially enhanced by the availability of wide angle and telephoto lens systems in addition to normal lens systems. Such lenses should be at least of the quality of the trioptiscope lens provided hitherto in order to be adequate for motion picture photography.